High alkali glass composition

ABSTRACT

A glass composition useful in preparing fiberglass comprises 12 to 25 weight % CaO; 12 to 16 weight % Al 2 O 3 ; 52 to 62 weight % SiO 2 ; 0.05 to 0.8 Fe 2 O 3 ; and greater than 2 up to about 8 weight % alkali metal oxide.

BACKGROUND

The majority of all continuous filament fiberglass is made from E-glassand used in applications such as fiber reinforced plastics and non-wovenmat for roofing reinforcement. Historically, E-glass was developed as alow electrical conductivity glass, giving it the “E” designation for“electrical”. To achieve low conductivity, the total alkali content,commonly designated as R₂O (Na₂O, K₂O, and Li₂O), had to be very low.The lack of R₂O, which is a good flux, was compensated by a largepercentage of alkaline earth oxide (CaO, MgO), which is a weaker flux.The composition was developed around a eutectic in the SiO₂—Al₂O₃—CaOsystem. Some of the CaO was replaced by MgO, and B₂O₃ was added to helplower the viscosity. The resulting composition space, known as E-glass,has an ASTM specification, D-578-05, to designate the standardcomposition ranges, shown in Table 1. Early patents in this compositionrange were relatively high in B₂O₃ and include U.S. Pat. Nos. 2,334,961and 2,571,074.

TABLE 1 Printed Circuit Boards and Aerospace Weight % General Weight %B₂O₃  5 to 10 B₂O₃  0 to 10 CaO 16 to 25 CaO 16 to 25 Al₂O₃ 12 to 16Al₂O₃ 12 to 16 SiO₂ 52 to 56 SiO₂ 52 to 62 MgO 0 to 5 MgO 0 to 5 Na₂O +K₂O 0 to 2 Total Alkali 0 to 2 TiO₂   0 to 0.8 TiO₂   0 to 1.5 Fe₂O₃0.05 to 0.4  Fe₂O₃ 0.05 to 0.8  F₂   0 to 1.0 F₂   0 to 1.0

Because of the very good water durability and fiberizability of E-glass,it became the composition of choice for general-purpose continuousfilament glass fiber. The ASTM composition ranges, especially forgeneral applications, are relatively wide, except for alkali (R₂O), andcan consist of glasses with a wide range of properties.

For E-glass, the most expensive raw materials are those that supplyboron (such as borax, boric acid, Ulexite, and Colemanite) and thesematerials can comprise one-third or more of the total raw material costeven though the B₂O₃ content in the glass is below 10%. One factoradding to the cost of boron in E-glass is the very low alkali (R₂O)content, which necessitates replacement of borax with higher cost boricacid unless colemanite is a viable alternative. The trend over the lastseveral decades has been to reduce the B₂O₃ content in E-glass for rawmaterial cost savings but the trade off typically comes in the form ofhigher melting temperatures and higher melt viscosity. Higher meltviscosity results in higher fiberization temperatures, represented bythe temperature at which the viscosity of the melt is equal to 1000poise and designated by T_(log3). An example of a low boron E-glasspatent is U.S. Pat. No. 7,022,634 and an example of an essentially“boron-free” E-glass patent is U.S. Pat. No. 5,789,329.

The use of recycled glass, known as cullet, is common practice inglasses melted for production of insulation wool and glass containers,but not for E-glass. Cullet can be broken down into two categories:pre-consumer and post-consumer. The most common grade of pre-consumercullet available is known as plate cullet, while the most common gradeof post-consumer cullet is a mixture of green, amber, and flint (clear)crushed bottles, referred to as “three-mix”. The majority ofcommercially available pre-consumer and post-consumer cullet has 12-16%R₂O, limiting the amount that could be used as a raw material forE-glass, due to the low total alkali metal oxides content of 0 to 2weight % in E-glass formulations.

With the limit of 2% total alkali, E-glass produced with a three-mixcullet containing 13.9% R₂O could only consist of a maximum of 11 weight% recycled content from the cullet. Glass recycling not only uses lessenergy than manufacturing glass from sand, limestone, and otherprocessed minerals, but also saves emissions of carbon dioxide, agreenhouse gas.

Table 2 below sets forth example compositions of plate cullet andthree-mix cullet.

TABLE 2 Glass Oxides Plate Three- (weight %) Cullet mix SiO₂ 72.4 72Al₂O₃ 0.3 2.0 Fe₂O₃ 0.2 0.25 B₂O₃ 0 0 Na₂O 13.8 13.2 K₂O 0.08 0.7 CaO9.3 10.7 MgO 3.6 0.8 F₂ 0 0

It is an object of the present application to provide a glasscomposition which gives technologists greater flexibility in designingglass compositions for a wide range of glass properties and low costproduction. More particularly, it is an object of the presentapplication to provide a glass composition which allows for increasedamounts of recycled glass, resulting in less greenhouse gas emissionsand a decrease in the amount of material going to landfills.

SUMMARY

In accordance with the foregoing objectives, provided is a glasscomposition useful in preparing fiberglass comprising:

12 to 25 weight % CaO, for example, 16 to 25 weight % CaO;

12 to 16 weight % Al₂O₃;

52 to 62 weight % SiO₂;

0.05 to 0.8 Fe₂O₃; and

greater than 2 up to about 8 weight % alkali metal oxide.

The total alkali metal oxides content of greater than 2 up to about 8weight % allows for incorporation of up to 55 weight % recycled contentin the glass composition in the form of cullet.

DETAILED DESCRIPTION

The presently disclosed glass composition useful in preparing fiberglasscomprises:

12 to 25 weight % CaO, for example, 16 to 25 weight % CaO;

12 to 16 weight % Al₂O₃;

52 to 62 weight % SiO₂;

0.05 to 0.8 Fe₂O₃; and

greater than 2 up to about 8 weight % alkali metal oxide.

In comparison to the ASTM specification for E-glass having a CaO contentof 16 to 25 weight %, the addition of alkali metal oxide above 2 weight% can be accompanied by a reduction in CaO, and therefore, the CaOcontent of the presently disclosed glass composition can be as low as 12weight %. The presently disclosed glass composition can furthercomprise:

B₂O₃ in an amount up to 10 weight %;

MgO in an amount up to 5 weight %;

TiO₂ in an amount up to 1.5 weight %; and/or

fluoride in an amount up to 1.0 weight %.

The alkali metal oxide of the presently disclosed glass composition cancomprise one or more alkali metal oxides selected from the groupconsisting of Na₂O, K₂O, and Li₂O. The presently disclosed glasscomposition can comprise Li₂O in an amount up to 5 weight %.

Advantages of the presently disclosed high alkali content glasscompositions include more effective electrical melting; higher usage ofrecycled glass (cullet); lower precious metal usage for fiberization,possibly non-precious metal bushings; longer bushing life; moreflexibility in batch materials (borax to replace boric acid, feldspar toreplace clay); and reduction in boron content without increasingT_(log3). With higher alkali content there is a need to balance waterdurability with T_(log3) but for many applications E-glass isover-designed for water durability.

In particular, the total alkali metal oxides content of greater than 2up to about 8 weight % allows for incorporation of larger amounts ofrecycled glass, for example, commercially available cullet product, ascompared to E-glass compositions. While a glass composition limited to 2weight % alkali metal oxides content can consist of up to 11 weight %recycled content, a glass having up to about 8 weight % alkali metaloxides content can consist of up to 55 weight % recycled content.Accordingly, the presently disclosed glass composition provides greaterflexibility in designing glass compositions for a wide range of glassproperties and low cost production, and results in less greenhouse gasemissions and a decrease in the amount of material going to landfills.

The presently disclosed glass composition allows for a wide range ofB₂O₃ content, which gives a wide range of fiberization properties. Inparticular, reduced B₂O₃ content permits one to realize cost savingsassociated with lower batch costs and abatement requirements. At thesame time, employing the presently disclosed glass composition allowsone to also achieve the cost savings without significantly increasingthe energy required for melting the glass, reducing fiberizationefficiency, or requiring a development of new bushing technology.

Two glass properties that are of importance to manufacturing are theT_(log3) and liquidus (crystallization) temperature. The T_(log3) is thetemperature at which the glass melt viscosity is equal to 1000 poise,corresponding to the temperature of fiberization, and in part iscorrelated to the energy required for melting and fiberization. Theliquidus temperature represents the upper temperature limit forcrystallization to occur.

In the production of fiberglass, the molten glass in the bushing istypically maintained at or above the T_(log3) for optimum fiberizationefficiency. A glass composition with a higher T_(log3) requires moreenergy to achieve this viscosity and therefore, incurs higher energycosts. In fiberglass production, it is preferred that the glass melt bemaintained at a temperature at least 100° F. above the liquidus to avoidcrystallization problems (in bushings or forehearth) and consequently,lower fiberization efficiencies. It has been found that in thecommercial production of E-glass fibers, fiberization efficiency issignificantly reduced as the difference between T_(log3) and liquidus(referred to as “Delta T”) falls below approximately 100° F. andcertainly when the difference falls below 50° F.

In an embodiment, the T_(log3) of the presently disclosed glasscomposition is less than 2300° F., for example, less that 2250° F., lessthan 2220° F., less than 2200° F., or less than 2160° F. In anembodiment, the liquidus temperature of the glass composition is atleast 100° F. less than that of the T_(log3) temperature (for example,at least 140° F. less than the T_(log3) temperature, at least 150° F.less than the T_(log3) temperature, or at least 160° F. less than theT_(log3) temperature), to therefore provide a Delta T of at least 100°F. Thus, the liquidus temperature is generally at least below 2150° F.,for example, less than 2100° F. or less than 2000° F.

The presently disclosed glass composition allows one to take advantageof the cost benefits associated with relatively lower B₂O₃ content, butavoid the disadvantages of crystallization and fiberization problems. Inparticular, the presently disclosed glass composition yields a glasswith a suitable T_(log3) and maintains a Delta T of at least 100° F.,while utilizing a relatively lower B₂O₃ content. In an embodiment, thepresently disclosed glass composition comprises about 3.5 to about 5.5weight % B₂O₃.

The presently disclosed glass composition allows for increased glassconductivity for increased electrical boost usage in melting providingfor more efficient energy utilization in the melting process. Inparticular, increased amounts of recycled glass in the presentlydisclosed glass composition provides for higher glass conductivity formore efficient use of electric boost in glass melting furnaces.

Increased amounts of recycled glass in the presently disclosed glasscomposition also decreases melt energy and results in less green housegas emission from the process. There are three main mechanisms by whichthe combination of cullet use and greater R₂O can decrease green housegas emissions. In the presently disclosed glass composition, theadditional R₂O allows the amount of CaO in the glass to be decreased. Acommon source of CaO in a glass batch is limestone, which can consist ofgreater than 40% CO₂. By reducing the amount of CaO required in theglass, the amount of limestone used is reduced, along with itsassociated CO₂ emissions.

By increasing R₂₀, additional cullet can be used in the glass batch.Since cullet is a source of CaO but contains no CO₂, it supplants someof the limestone used to create the glass, further reducing the CO₂emitted during production.

By increasing the use of cullet, the energy required to melt the glassbatch is reduced. If the energy source is natural gas or electricityproduced by the burning of natural gas and/or coal, then reducing theenergy usage will also result in CO₂ reductions.

E-glass is typically melted in gas-fired glass furnaces. In thesefurnaces, the burning of natural gas provides the majority of the energyto melt the glass while electricity can be used to supplement thenatural gas. The use of electricity to melt E-glass is currently limitedby the low electrical conductivity of the glass. By increasing theamount of R₂O in the glass, the electrical conductivity of the glasswill improve which will increase the proportion of energy which can besupplied by electricity. Since electricity can be created withoutcreating CO₂ via nuclear, wind, solar, and geo-thermal methods,increasing the amount of melt energy supplied by electrical could resultin additional CO₂ reductions. Furthermore, since electrical boost ismore efficient at delivering energy for glass melting, less total energyis required when the proportion of electrical energy to natural gasenergy is increased.

Fiberization is typically accomplished by drawing fibers though amulti-orifice bushing plate made from precious metals such as platinumand rhodium. These metals tie up a significant dollar value and aresubject to large market price fluctuations. The amount of precious metalrequired for a given throughput is dependent on the T_(log3) of theglass with higher T_(log3) glasses requiring thicker bushings and/orshorter bushing service life. Reducing the T_(log3) can result insignificant savings by reducing the amount of precious metal in serviceand/or increasing bushing service life. Reducing T_(log3) also opens upthe possibility of utilizing non-precious metals for bushings.

In an embodiment, the presently disclosed glass composition has aviscosity and fiberization temperature that is sufficiently low torealize reasonable fiberization rates and efficiencies in without theuse of expensive precious metal alloys (typically Pt—Rh alloy) as thebushing material. Thus, in a method of preparing fiberglass using thepresently disclosed glass composition, a non-Pt/Rh bushing is employed.

The following examples are intended to be exemplary and non-limiting.

EXAMPLES

Table 3 below sets forth examples of the presently disclosed glasscomposition.

TABLE 3 Glass Oxides Comparative Comparative (weight %) Example 1Example 2 Example A Example B Example C Example D Example E SiO₂ 55.060.0 55.5 57.6 56.7 54.7 54.4 Al₂O₃ 13.6 13.2 13.7 13.8 13.7 13.6 13.6Fe₂O₃ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 TiO₂ 0.5 0.5 0.5 0.5 0.5 0.5 0.5 B₂O₃4.9 0.0 4.9 4.2 4.1 6.7 8.4 Na₂O 1.8 0.6 5.1 5.1 5.1 3.0 3.0 K₂O 0.1 0.10.1 0.1 0.1 0.1 0.1 R₂O 1.9 0.7 5.2 5.2 5.2 3.1 3.1 CaO 22.0 22.3 17.917.0 17.9 18.7 17.3 MgO 1.8 3.1 1.9 1.5 1.5 2.3 2.4 T_(log3) (° F.) 21682298 2170 2235 2207 2155 2147 Liquidus (° F.) 2027 2159 2030 2058 20782004 1942 Delta T (° F.) 141 139 140 177 129 151 205

The glasses of Table 3 were prepared by melting in lab scale quantitiesand physical properties were measured. Comparative Examples 1 and 2 areexamples of E-glass from U.S. Pat. Nos. 7,022,634 and 5,789,329,respectively. Examples A through C are glasses of the presentlydisclosed glass composition that contain approximately 5% R₂O and fallwithin the desirable range for T_(log3), liquidus, and Delta T. ExamplesD and E are glasses of the presently disclosed glass composition thatcontain approximately 3% R₂O and fall within the desirable range forT_(log3), liquidus, and Delta T. In addition, experimentation has shownthe trend that increases in alkali content can be effectivelyaccompanied by decreases in CaO content. Therefore, at the high end ofthe alkali range for the present invention it would be reasonable tohave CaO levels below 16%. It would also be reasonable to have CaOlevels as low as 12%, especially in formulations with higher amounts ofB₂O₃ content.

While various embodiments have been described, it is to be understoodthat variations and modifications may be resorted to as will be apparentto those skilled in the art. Such variations and modifications are to beconsidered within the purview and scope of the claims appended hereto.

1. A glass composition useful in preparing fiberglass comprising: 12 to25 weight % CaO; 12 to 16 weight % Al₂O₃; 52 to 62 weight % SiO₂; 0.05to 0.8 Fe₂O₃; and greater than 2 up to about 8 weight % alkali metaloxide.
 2. The glass composition of claim 1, comprising 16 to 25 weight %CaO.
 3. The glass composition of claim 1, further comprising B₂O₃ in anamount up to 10 weight %.
 4. The glass composition of claim 1, furthercomprising MgO in an amount up to 5 weight %.
 5. The glass compositionof claim 1, further comprising TiO₂ in an amount up to 1.5 weight %. 6.The glass composition of claim 1, further comprising fluorine in anamount up to 1.0 weight %.
 7. The glass composition of claim 1,comprising greater than 5 weight % recycled glass.
 8. The glasscomposition of claim 7, comprising up to 55 weight % recycled glass. 9.The glass composition of claim 1, comprising up to 55 weight % recycledglass.
 10. The glass composition of claim 1, wherein the alkali metaloxide comprises one or more alkali metal oxides selected from the groupconsisting of Na₂O, K₂O, and Li₂O.
 11. The glass composition of claim 1,comprising Li₂O in an amount up to 5 weight %.
 12. The glass compositionof claim 3, comprising about 3.5 to about 5.5 weight % B₂O₃.
 13. Theglass composition of claim 1, wherein the glass composition has aT_(log3) temperature of less than 2300° F.
 14. The glass composition ofclaim 1, wherein the glass composition has a T_(log3) temperature ofless than 2220° F.
 15. The glass composition of claim 1, wherein theglass composition has a T_(log3) temperature of less than 2160° F. 16.The glass composition of claim 1, wherein the glass composition has aliquidus temperature at least 100° F. less than the T_(log3) temperatureof the glass composition.
 17. The glass composition of claim 1, whereinthe glass composition has a liquidus temperature at least 140° F. lessthan the T_(log3) temperature of the glass composition.
 18. The glasscomposition of claim 1, wherein the glass composition has a liquidustemperature at least 160° F. less than the T_(log3) temperature of theglass composition.
 19. A method of preparing fiberglass using the glasscomposition of claim
 1. 20. The method of claim 19, comprising employinga non-Pt/Rh bushing.